Boolean modifier cannot be executed error
Your mesh is open, and that is when the Boolean modifier will start to complain. You have to close the mesh. When you mentioned that parts of the mesh are showing through, it proves that your mesh is open. To fix this, you should redo the whole process, perhaps with a less complex font to make sure weird things do not happen to your mesh (that is if you are using another font apart from the default). Hope this helped!